This invention is related to an essentially instantaneous method for determing whether a polymeric food or beverage container has been exposed to certain contaminants. The discussion below will focus on beverage containers but the invention is also applicable to food containers.
Polymeric beverage containers that are potentially reusable and refillable are in use for a wide variety of soft drink beverages such as "Coke", "Diet Coke", "Pepsi", "Diet Pepsi", "7 Up", "Dr. Pepper", root beer, cream soda, "Sprite", "Regular Slice", "Diet Slice", gingerale and the like. It is expected that beer and other alcoholic beverages will be sold in reusable polymeric beverage containers in the future. Currently, billions of polymeric containers are used worldwide and their use is expected to grow.
These containers are formed from copolymers of acrylonitrile, polyethylene terephthalate (PET), amorphous nylon and multilayer composites, as well as more common moldable resins such as polyethylene and polypropylene. Unlike glass containers which do not absorb contaminants and are relatively easy to clean, the polymeric beverage container will absorb contaminants placed in the container. For example, pine oil or lemon oil will be absorbed by the polymeric container structure and when a beverage is placed in the container the contaminant will leach out into the beverage and impart the beverage with an off taste. A more serious problem arises when toxic substances are placed in the polymeric container such as lindane, parathion and the like. These substances are also absorbed by the polymeric container and can later leach into a beverage placed into the container. This problem has effectively precluded the widespread commercial reuse of polymeric containers.
Nevertheless, in order to conserve energy, materials and waste disposal space, the food and beverage industries in several countries are planning to begin to reuse these plastic containers. A major impediment to this effort lies in the difficulty of determining whether the polymeric container has been contaminated.
Prior art automatic inspection systems for beverage containers focus upon surface defects or residual liquid left in the container. For instance, there are inspection systems such as described in U.S. Pat. No. 4,459,023 issued to Reich et al on July 10, 1984, that determine if the container has dust, contamination or cracks on the container surface using a polarized scanned optical beam and an array of polaroid optical detectors. Other automatic inspection systems such as described in U.S. Pat. No. 4,368,980 issued to Alfred et al on Jan. 18, 1983 detect the presence of residual product or liquids, e.g., water and oil, remaining inside the container using the absorption of infrared radiation by water. Other prior art in this area focus upon color changes of a strip or cell exposed to a specific substance or atmosphere (e.g., ethylene oxide, steam, water, normal atmospheric conditions, etc.). In these references, the detection method is based upon visually sensing the change in color or configuration. None of the prior art inspection systems use a sensor attached to the inside of the container which is later illuminated with ultraviolet (UV) light to essentially instantaneously detect whether a number of different contaminants have potentially leached into the structure of a polymeric container.
In order to allow the large scale commercial reuse of polymeric food or beverage containers, there is a need for a method of detecting whether or not a polymeric container has been exposed to contaminants. Obviously, expensive analytical techniques and equipment can be used to analyze for contaminants but to be useful and practical the method must be inexpensive, essentially instantaneous and provide for easy and simple detection of a wide variety of contaminants.